This invention relates to a ground proximity warning systems and more particularly to ground proximity warning systems for helicopters.
Ground proximity warning systems, or GPWS, provide aural and visual warnings of terrain features that indicate when the aircraft is or will be in potentially hazardous proximity to terrain, or when a flight condition exists that is apparently inconsistent with the aircraft""s position relative to terrain. The early generation ground proximity warning systems use a radar altimeter to sense dangerous proximity to terrain. The radar altimeter senses both the proximity of the terrain and the rate by which that proximity or height above ground changes. The rate of proximity change is significant when compared to a predefined envelope to determine if a dangerous condition exists. Classic GPWS systems also contain additional alert functions called xe2x80x98modesxe2x80x99 that alert to other potentially hazardous conditions based on flight regime.
GPWS devices have significantly enhanced the safety of commercial, military, and general aviation, but suffer from some limitations. Because GPWS systems lack a terrain information database, GPWS has only a limited ability to anticipate terrain hazards ahead of the aircraft. Thus, later generation GPWS devices, called EGPWS devices or terrain awareness and warning systems (TAWS), include a stored terrain database. An EGPWS compares the position of the aircraft in three-dimensional space with the stored terrain information to identify potential conflicts. Diminishing the reliance upon radar altimetry as the sole determinant of hazardous proximity has enhanced the EGPWS ability by giving the alerting envelope a significant look-ahead functionality. With the ability to anticipate the significant terrain hazards ahead, the EGPWS plots the anticipated path of the aircraft and alerts the pilot when a terrain avoidance maneuver is necessary. EGPWS devices may also include all the functionality and modes of the classic GPWS devices.
Nuisance warnings detract from the utility of the EGPWS. Nuisance warnings are warnings generated by the EGPWS that do not reflect an actual hazard. Such warnings may occur for a variety of reasons such as unique terrain features that trigger the alert without actually endangering the aircraft. When nuisance alerts become frequent, flight safety is compromised, because the pilot will either turn off the EGPWS or learn to ignore it. Refined EGPWS systems minimize nuisance alerts through the use of an absolute cutoff altitude, which is dynamically determined from surrounding terrain characteristics and aircraft flight parameters. Below the absolute cutoff altitude, all terrain proximity alerts are suppressed.
In the context of rotary winged aircraft, such as helicopters, many fixed-wing EGPWS assumptions may not hold true. The fixed-wing EGPWS assumes the aircraft can climb at a maximum finite angle, such as six-degrees to avoid terrain. However, many rotary wing aircraft can climb vertically or hover. In a helicopter, a fixed-wing EGPWS will alert unnecessarily during hovering flight near terrain. Similarly, merely setting the assumed maximum flight angle in a fixed-wing EGPWS to vertical would render the device non-functional, because no terrain alerts, including valid ones, would issue.
One fixed-wing EGPWS, manufactured by Honeywell International Inc., stores runway location and elevation information in its terrain database. The fixed-wing EGPWS uses the installed terrain database to generate an alert when the aircraft approaches terrain where there is no runway available. The fixed-wing EGPWS assumption that landing and take-off require proximity to an airport runway is valid for fixed wing aircraft. However, it is common practice for helicopter operators to fly into and out of non-airport environments. In such normal flight situations, a fixed-wing EGPWS would issue a nuisance alert.
Similarly, fixed-wing EGPWS systems suppress the display of all terrain features that lie below the absolute cutoff altitude in order to reduce display clutter. The use of the same absolute cutoff altitude for both alert and display stems from the assumption that fixed-wing aircraft intentionally operate near terrain only in the vicinity of airport runways. This assumption does not hold for rotary wing aircraft that routinely operate near terrain away from airports. In those situations, a fixed-wing EGPWS may not adequately display terrain features when such display would be a useful avoidance tool for the pilot.
The foregoing discussion highlights the need for modifications in the EGPWS warning and display algorithms to enhance its flight safety benefits to rotary-winged aircraft.
The present invention is an improved EGPWS system, method, and computer program product that reduces terrain proximity nuisance alerts in a highly maneuverable aircraft, such as a helicopter. The system or apparatus comprises a novel use of an aircraft speed signal to determine an absolute cutoff altitude, where terrain lying below the absolute cutoff altitude will not generate a ground proximity alert. The apparatus further comprises a database of stored terrain information, a signal-processing device, and an output. Where, for example, a present art EGPWS system might generate a warning on a slow approach of the aircraft to an off-runway landing site, the present invention will suppress that warning. Thus, the present invention enhances flight safety by presenting a more reliable indicator of the actual terrain hazard in such aircraft.
According to another aspect of the present invention, the invention exists as a system, method, and computer program product for the enhanced display of terrain proximate a low-flying rotary wing aircraft. Where, for example, a present art EGPWS system suppresses the display of terrain lying below the absolute cutoff altitude, the present invention allows for an expanded display of terrain relative to the lowest terrain elevation in the selected display area. The present invention accomplishes this by defining different absolute cutoff altitudes for alert detection and for display.
Further details and operation of the present invention will be described below with reference to the drawings. In the lexicon of the present invention, terrain encompasses both natural terrain features and man-made obstacles located on the ground.